Geoscience Reference
In-Depth Information
indeed it is the current theory of quantum mechanics that underpins our understanding of
the fluorescence process.
1.2 The Relevance of Quantum Mechanics and Electronic Theory
Wave-particle duality is a central concept for our current understanding of modern quan-
tum mechanics (Anastopoulos,
2008
). The fact that particles and matter exhibit both wave
and particle-like properties helps us to explain their behavior at the quantum scale. To
appreciate
how
light interacts with matter, it is important first to consider the nature of light
and the role of matter in terms of electronic structure. Unfortunately, an in-depth discussion
pertaining to quantum theory and the magnificent discoveries throughout the history of sci-
ence is beyond the scope of this chapter. However, for readers to gain an insight into
how
light can interact with matter in ways that result in the emission of light it is necessary first
to consider the nature of light and how matter is organized in terms of electronic structure.
Although there have been monumental discoveries over the ages, all of which have contrib-
uted to our understanding of the universe, for simplification this chapter focuses attention
toward scientific discoveries achieved throughout late 19th and the 20th centuries.
1.2.1 Wave-Particle Duality and Quantization of Energy and Matter
During the early 19th century, atoms were the smallest particles known, and were believed
to be indestructible and indeed indivisible, as such the knowledge of subatomic particles
and their role in energy transfer processes in light-matter interactions were unknown.
Many of the early advancements in electromagnetic theory were achieved owing to curios-
ity surrounding the phenomena of magnetism, electricity, and light.
1.2.1.1 Subatomic Particles
In 1838, Michael Faraday passed an electric current through a glass tube containing rare-
fied air (partially emptied). Faraday observed an arc of light emanating from the negative
electrode (cathode) almost reaching the positive electrode (anode). These so-called cathode
rays, what we now know to be electron beams, were the subject of great interest (Faraday
1844
; Dahl,
1997
). Shortly after the work of Faraday, in 1839, the French physicist Edmund
Becquerel, who was fascinated by the properties of light, observed that certain materi-
als produced electricity (the emission of electrons) when exposed to sunlight (Becquerel
1839
). In 1857, German physicist Heinrich Geissler repeated Faraday's experiment but
this time he was able to evacuate more air from specially designed glass tubes (10
−3
atmos-
pheres) using an improved pump. Geissler found that, instead of an arc, the light glow
filled the tube completely (Dahl,
1997
). James Clerks Maxwell's work regarding the nature
of electromagnetic fields paved the way for a greater understanding of the nature of light,
and between 1862 and 1864 Maxwell demonstrated that electric and magnetic fields prop-
agated through space, in wave forms, at the speed of light. From this, Maxwell deduced
(Maxwell's equations) that electricity, magnetism and light were all manifestations of the
